Methods of obtaining sintered beryllium oxide



Unite States Patent fllice 3,057,684

Patented Oct. 9, 1962 when subjected to the conditions, in particular of tem- 3,057,684 METHODS OF OBTAINING SINTERED perhlture, at which sintering takes place, must be berylhum BERYLLIUM OXIDE X1 Emile Pruvot, St. Jean de Maurienne, Paul Baradez, La A preferred addition product, which is particularly Praz, Roger: Caillat, Sevres, and Roger Pointud, Paris, satisfactory, is beryllium sulfate.

fame, flsslgllms t0 commlssalzlat a lEllergle Atom! The paste thus obtained is then dried and calcined either e! a French society 4 successively or in a single operation. Calcination is con- No Drawmg' Filed June 1956 599,331 ducted in such manner as to leave in the beryllium oxide Claims priority application France June 29 1955 h (Cl 23 183) that is obtained some amount (more than 1%) of the l0 anion of the incorporated salt or acid. In order to obtain The present invention relates to methods for the obthis result, it is necessary to avoid too long a calcination tainment of sintered beryllium oxide. or a calcination at too high a temperature, such that the Its chief object is to provide the sintering conditions decomposition of the added substance would be total. and also to permit of obtaining sintered products which According to another embodiment of the invention,

are of a high purity, very regular and of a density close the mineral acid or corresponding salt of beryllium is to the theoretical density, which is of great interest in added directly to the beryllium oxide, in particular after nuclear applications. calcination of the beryllium hydroxide from which it is There are known methods of obtaining sintered 'berylobtained. lium oxide of a good consistency which consist in start- Beryllium oxide obtained as above stated is the product ing from a beryllium hydroxide or a beryllium sulfate, used for sintering under pressure. One of the advantages drying it and calcining it, the beryllium oxide thus obof this product is its relatively high density, which facilitainecl being subsequently sintered. tates the filling of the sintering mold by said oxide in the The methods known up to this time have many draw powder form. backs. In particular, calcination of a beryllium hydrox- The addition of an acid or a beryllium salt as above ide which does not comply with particular conditions described permits of conducting sintering under pressure gives rise to important losses due to the fact that beryllium at a temperature, a pressure, and during a time which are oxide or beryllium hydrate is carried along by the water susbtantially lower than the temperature, pressure and vapor evolved by dehydration This involves very seritime necessary for obtaining products of equivalent qualious difliculties due first to the low yield and also to the ties in the absence of such an addition Furthermore the very expensive protection means which are made necesmethod according to our invention permits of obtaining sary by the toxicity of the beryllium compounds which sintered products of a very high density close to the theare thus carried along. oretical density and of a very high purity so as to per- Furthermore, the amorphous and alpha forms of berylmit nuclear applications of such products. lium hydroxide are very difiicult to wash so that they do These two advantages (to wit high density and high not permit, when they consitute the starting material, of purity) are generally, in the conventional methods, inobatining a sintered product of high purity. compatible with the general conditions under which 8. Finally, the amorphous and alpha forms of beryllium good sintering is possible (to wit temperature, pressure hydroxide give, when calcined, oxides which it is diflicult and duration relatively low). to sinter under high pressure unless they have been pre- The sintered products obtained by our method are of j liminarily calcined to very high temperature. Sintering a homogeneous density Whatever be the dimensions of the of such oxides calls for conditions of temperature, presproduct, they are free from mechanical defects such as sure and duration which are very difiicult to comply with cracks, holes, etc. and the sintered product that is finally obtained generally Finally, the method according to our invention permits has defects such as cracks and the like. a great range of adjustment of the general conditions of On the contrary, the beta form of beryllium hydroxide sintering, which is suflicient to permit a high regularity is a dense precipitate which can easily be filtered. It manufacture. can be brought, by successive washings, to a very high We will now describe some examples of a specific degree of purity. method according to our invention, these examples having According to our invention, the product that is subno limitative character. jected to the sintering operation consists of anhydrous beryllium oxide resulting from the calcination of a beryl- Example I hum hydroxlcle lefast most of which 15 m the beta e We start from 275 kg. of precipitated beryllium hydroxand mixed h e htfle more than 1 Percent of amons ide filtered in the moist state and containing 95% of of a mineral acid in the form of a beryllium salt the only B60 in the beta form We add thereto in a mixing e e of h when suhleeted f the slhtenng e paratus, 37.5 kg. of tetrahydrate beryllium sulfate. tions, in particular of temperature, is beryllium oxide. The Pasta that is obtained is spread on the Plates of a Beryllium hydroxlde m h beta form may be e furnace, dried, and calcined at 1000" until its ignition loss for instance, as described in the paper by A. Seitz et al. is a little above g Q 261 9), Pages and If an already calcined beryllium oxide is available in the Pubhcahohs referred to h the pure state, we may add thereto a little more than 1% In a first emhedlmeht of the Invention the mlhal of an anion of a mineral acid in the form of a beryllium beryllium hydroxide (at least mostly of the beta form) Salt is given the form of a Paste, by addition of a mineral The product thus obtained is sintered under load, acacid or of the beryllium salt corresponding to such an acid. di t one of th known th d at a tem t e These addition products may be used either in the dry 60 of 1780 C and under a pressure 0f170 kg, per sq cm state or in solution. for two hours. The sintered product finally obtained has The salt or acid thus added is preferably chosen so that a specific gravity of 2.95. this salt or the salt resulting from the action of this acid Analysis of the sintered product showed that the acid quickly dissociates at a temperature at most equal to the ion that was added has completely disappeared and the temperature of total dehydration, in their presence, of purity of the product was higher than that of the starting beryllium hydroxide. Furthermore their only residue, material.

Example 11 We start from 164 kg. of filtered beryllium hydroxide containing 80% of B60 in the beta form and 20% in the alpha form. They are mixed with 100 kg. of a solution at 37.5% of a beryllium sulfate.

The paste thus obtained is placed in a continuous drying apparatus which delivers the dried product in a continuous fashion into a calcination furnace.

Then sintering is carried out as in the preceding example.

Example III To 250 kg. of beryllium hydroxide in the beta form we add 160 kg. of a 14% solution of beryllium chloride in a mixing appartus in order to obtain a paste which is subsequently dried, calcined and sintered as described in the preceding examples.

What we claim is:

1. A method of preparing sintered beryllium oxide of high density and purity comprising adding a mineral acid selected from the group of hydrochloric acid and sulfuric acid to beryllium hydroxide at least 80 percent of which is in the beta form, thereby converting part of said beryllium hydroxide to the beryllium salt of said acid, heating the salt-hydroxide mixture to form a beryllium oxide containing still a little more than about 1 percent of said salt, calculated on the total mixture, and subsequently sintering the mixture, thereby obtaining sintered beryllium oxide free of said salt.

2. A method of preparing sintered beryllium oxide of high density and purity comprising adding a mineral acid selected from the group consisting of hydrochloric acid and sulfuric acid to beryllium oxide obtained by calcination of beta beryllium hydroxide at least 80 percent of which is in the beta form, heating the salt-oxide mixture to form a beryllium oxide containing still a little more ed., pp. 224-227, Longmans, Green &

than about 1 percent of said salt, calculated on the total mixture, and subsequently sintcring said mixture, thereby obtaining sintered beryllium oxide free of said salt.

3. A method of preparing beryllium oxide of high density and purity comprising adding a beryllium salt of an acid selected from the group consisting of hydrochloric acid and sulfuric acid to beryllium hydroxide at least percent of which is in the beta form, heating the mixture to form a beryllium oxide containing still a little more than about 1 percent of said salt, and subsequently sintering the mixture, thereby obtaining sintered beryllium oxide free of said salt.

4. A method of preparing beryllium oxide of high density and purity comprising adding a beryllium salt of a mineral acid selected from the group consisting of hydrochloric acid and sulfuric acid to beryllium oxide obtained by the calcination of beryllium hydroxide at least 80 percent of which is in the beta form, heating the mixture to form a beryllium oxide containing still a little more than about 1 percent of said salt, and subsequently sintering the mixture, thereby obtaining sintered beryllium oxide free of said salt.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES I. W. Mellors Inorg. and Theo. Chem, vol. 4, 1923 00., New York, 

1. A METHOD OF PREPARING SINTERED BERYLLIUM OXIDE OF HIGH DENSITY AND PURITY COMPRISING ADDING A MINERAL ACID SELECTED FROM THE GROUP OF HYDROCHLORIC ACID AND SULFURIC ACID TO BERYLLIUM HYDROXIDE AT LEAST 80 PERCENT OF WHICH IS IN THE BETA FORM, THEREBY CONVERTING PART OF SAID BERYLLIUM HYDROXIDE TO THE BERYLLIUM SALT OF SAID ACID, HEATING THE SALT-HYDROXIDE MIXTURE TO FORM A BERYLLIUM OXIDE CONTAINING STILL A LITTLE MORE THAN ABOUT 1 PERCENT OF SAID SALT, CALCULATED ON THE TOTAL MIXTURE, AND SUBSEQUENTLY SINTERING THE MIXTURE, THEREBY OBTAINING SINTERED BERYLLIUM OXIDE FREE OF SAID SALT. 